Hydrogenation of dicyclodiene dicarboxylic acids



United States Patent HYDROGENATION OF'DICYCLODIENE DICARBOXYLIC ACIDSOber C. Slotterbeck, Rahway, Herbert K. Wiese, Cranford, and Addison W.Hubbard, Westfield, N. J., assignors to Esso Research. and: EngineeringCompany, a corporation of Delaware No Drawing. ApplicationlAugus't 19,1955 Serial No. 529,586

11 Claims. (Cl. 260-514 This invention relates to an improved processfor making hydrogenated dicyclodiene dicarboxylic acids such asdihydroand tetrahydro dicyclopentadiene dicarboxylic acid and saltsthereof.

Dicyclodiene dicarboxylic acids are well known materials. Theirpreparation is; described, for instance, in a copending Wieseapplication, :Serial No. 401,437, filed December 30, 1953, now U. S;Patent 2,781,397, patented February 12, 1957. In order to avoidduplication, the former application is incorporated herein by reference.By way of summary, however, let it suflice to indicate that the knownmethod involves in essence, first, the reaction of finely dividedmetallic sodium with monomeric cyclodiene such as cyclopentadiene in thepresence of an inert diluent such as xylene and. a small amount of anactivator such as anhydrous alcohol, second, the con version of theresulting cyclodienyl sodium to the disodium salt of dicyclopentadienedicarboxylic acid by treatment of the xylene solution with anexcess ofcarbon dioxide, third, addition of water to .form an aqueous solution ofthe disodium salt under inherently alkaline conditions, fourth,separation of the aqueous solution from the hydrocarbon phase, andlastly, acidificationof theaqueous solution with sulfuric or otherstrong acid to spring and precipitate the free dicyclodiene dicarboxylicacid from the solution.

The resulting dicyclodiene dicarboxylic acid, which is usually a mixtureof endo and exo isomers, has been found useful as a substitute forphthalic or rnaleic acids in a variety of reactions, as a startingmaterial in the manufacture of polyester type lubricants and resins, andparticularly in the manufacture of modified alkyd resins. However, inmany of these uses, the dicyclopentadiene dicarboxylic acid has hadvarious shortcomings. For instance, the previously known acids, of thistypehave tended to undergo partial cracking, decarboxylation, as well asundesirable gellation when heated. As aresult, products preparedtherefrom by means. of high temperature reactions have lacked uniformityandsometimes; exhibited undesirably dark color.

The foregoing shortcomings have been alleviated to a varying extent byconverting the dicyclodiene dicarboxylic acids into the correspondinghydrogenated derivatives as described in a copending Cohen application,Serial No. 510,561, filed May 23, 1955. The previously proposed methodof preparing these hydrogenated derivatives generally involveddissolving the water-insoluble solid dicyclodiene dicarboxylic acid in asuitable organic solvent such as anhydrous ethanol, hydrogenation of'the dissolved acid in the presence of a hydrogenation catalyst such asplatinum, filtration to remove the catalyst, and recovery of thehydrogenated product by evaporation of the solvent.

However, this known preparation of the hydrogenated acids from thecorresponding dicyclodiene acids has been rather cumbersome and theresulting products have tended to be somewhat ofi color and odoriferous,at least in part due to the properties of the dicyclodiene acids used asstarting material.

It is the main object of the present invention to devise a simplerprocess for preparing the hydrogenated dicyclodiene dicarboxylic acidsand to produce them in more nearly colorless and odorless form. A morespecific object is to avoid the need for an extraneous organic solventand the evaporation thereof at the end'of the reaction. Still anotherobject is to prepare the hydrogenated acids from the cyclodienehydrocarbon feed by a process not requiring the isolation of thedicyclodiene dicarboxylic acid intermediates in solid form. Theseandother objects, as well as the nature, scope, operation and advantages ofthis invention will become more clearly apparent from the subsequentdescription and appended claims. In reading the description, it will beunderstood that all amounts, proportions and percentages of materialsare expressed on a weight basis unless indicated otherwise.

It has now been discovered that the desired hydrogenated acids can beprepared in a surprisingly effective manner and in a high state ofpurity by hydrogenating an alkali metal salt of the correspondingdicyclodiene dicarboxylic acid while dissolved in water, andparticularly in water at a carefully controlled hydrogen ionconcentration. As a result, if desired, the alkali metal salt of thedicarboxylated dicyclodiene as prepared in its original synthesis bycarboxylation of the cyclodienyl metal compound can be used directly inthe hydrogenation, without springing the intermediate free diene acid,butsimplyby extracting the hydrocarbon dispersion of the. carboxylatedsalt with water, preferably acidified water as hereafter explained, andhydrogenating the salt in the aqueous solution. After completion of thehydrogenation theudihydroor tetrahydro-acid can be precipitated as awater insoluble. solid by acidifying the aqueous, salt solution andseparated by filtration.

In brief, the invention is broadly usefultinrpreparing dihydroor'tetrahydro-derivatives of' dicycloperitadiene dicarboxylic acids whichmay be originally present either in the form of hydrocarbon dispersionsof the corresponding metal salts or in the form of the solid, free acid.More specifically it is of particular interest in preparing dihydroandtetrahydro-dicyclopentadiene-dicarboxylic acid, or their respectivesalts and esters, from the corresponding unsaturated sodium metal saltwhich can be represented for the present purposes by the followingformula:

The exact position of the two carboxyl groups on the cyclodiene dimermolecule is not definitely known. Contrary to earlier literaturereferences, recent work indicates that the carboxyl groups are attachedto carbon atoms adjacent to the double bonds, one on each ring. Ofcourse several isomers having such a structure are possible, althoughthe sharp melting point of the product indicates the presence of anessentially pure isomer, rather than a mixture.

At any rate, the exact structure is of no particular importance in thisinvention which is broadly applicable I to the hydrogenation of dimericcyclodienes having one carboxyl group attached to each cyclodienenucleus.

Of course, instead of using the sodium salt of the unsaturated acid, itis equally feasible to use in the hydrogenation any other water solublesalt, e. g. the potassium or lithium salt. The salt may initially be inthe form of a dispersion in an inert hydrocarbon such as xylene, whichis commonly used as a reaction medium in the synthesis of the salt fromthe original cyclodiene hydrocarbon, or the salt may be in solid form,obtained by filtering the original xylene slurry in an oxygen-freeatmosphere, or the salt may be in the form of an aqueous solution bestprepared by suspending the free dicarboxylated dicyclodiene acid inwater and then adding dilute alkali to the suspension in an amount suchthat the pH of the aqueous solution is kept below about 7.5 or 8. Whenthe salt is originally in the form of a hydrocarbon slurry, it, too,must be changed into an aqueous solution by extraction or mixing withwater and separation of the insoluble organic liquid from the aqueoussolution by decanting or the like. If the salt is used in thehydrogenation directly from the carboxylation step, without springingthe free dicarboxylated dicyclodiene acid and reforming the salt, it isadvisable to allow the salt to age for about to 360 minutes at about toC., after dissolving in Water, in order to insure that anymonocarboxylated monocyclodiene acid salt is completely converted intothe desired dimer form.

Obviously, in addition to the preparation of derivatives ofdicyclopentadiene dicarboxylic acid proper, the invention is similarlyapplicable to the preparation of hydro derivatives of the correspondinglower alkyl homologues such as dimethyldicyclopentadiene dicarboxylicacid, i. e., the dicarboxylated dimer of methylcyclopentadiene, andmethyldicyclopentadiene dicarboxylic acid, i. e., the mixed dimer ofcyclopentadiene carboxylic acid and methylcyclopentadiene carboxylicacid.

.The hydrocarbons, if any, in which the disodium salt of thedicyclodiene dicarboxylic acid may originally be suspended are thosecustomarily employed in the synthesis of the acid and more particularlyin the carboxylation of the cyclodienyl metal intermediate. Inerthydrocarbons boiling between about and C. such as xylene, toluene,benzene, cyclohexane, heptane, hexane, light naphthas, straight runmineral spirits are typical, as is already well known.

When making up the aqueous solution of the dicarboxylated dicyclodieneacid salt for the hydrogenation, whether by extraction of the organicslurry or by dissolving the separated salt, or by dissolving the freeacid in alkaline water, it has been found particularly advantageous tomaintain the hydrogen ion concentration of the alkali metal saltsolution at a pH between about 5.8 and 7.5, both before and during thehydrogenation step. Since the alkali metal salt of the dicarboxylateddicyclopentadiene acid normally gives aqueous solutions characterized bya pH value in excess of 8 or even 11, the preferred embodiment of theinvention requires the presence of suitable amounts of extraneous acidin the aqueous salt solution. Thisextraneous acid may be either a strongorganic acid such as formic, acetic, propionic, trifiuoroacetic, oxalic,etc., or a mineral acid such as sulfuric or phosphoric. Acidificationwith carbon dioxide or sulfur dioxide is also feasible, though somewhatless practical since it normally requires the use of pressure in orderto bring the hydrogen ion concentration to the required value.

A particularly efi'ective method of acidification involves adding ananhydrous acid such as glacial acetic acid directly to the hydrocarbonslurry of the dicarboxylated metal salt before an aqueous solution ismade therefrom. However, it is also feasible to add the extraneous aciddirectly to the Water phase, either before or after the dicarboxylateddicyclodiene metal salt is dissolved therein. The amount of extraneousacid required for the pH control may range from about 1 to 17 moleequivalents per 100 atoms of alkali metal present. The optimum amount ofacid will vary somewhat from case to case, depending primarily on theparticular homologue of dicyclodiene acid being treated, and can bereadily determined by simple preliminary trial. For instance, theoptimum pH value has been found to fall in the range between about 5.8and 7.5 when treating the dimeric carboxyl derivatives ofcyclopentadiene proper, whereas a somewhat higher pH value between about7.0 and 7.5 has been found best for the derivatives ofmethylcyclopentadiene.

If no extraneous acid is added and the aqueous solution is hydrogenatedunder more alkaline conditions than the optimum indicated above, theproduct tends to be somewhat dark in color and malodorous, and thereforenot so well suited for uses requiring light color and absence of odor.At the same time, however, it will be realized that hydrogenation of theaqueous salt solution at relatively alkaline conditions is feasible,gives useful products, and offers important process advantages over thepreviously known method involving hydrogenation of the acid in organicsolvents. On the other hand, the use of unduly acid solutions is notdesirable since this tends to cause precipitation of the solid, freeacid and thus impairs effectiveness of the hydrogenation.

The aqueous solution used in the hydrogenation step of this inventionmay contain the alkali metal salt in a concentration of about 5 to 35percent. Either the dihydrogenated or the tetrahydrogenateddicarboxylated dicyclodiene acids may be made therefrom, depending onwhether the amount of hydrogen allowed to react is sufiicient tohydrogenate one or both of the double bonds of the original diene acidmolecule. Actually, even when the tetrahydro product is being prepared,the reaction proceeds in two distinct stages and formation of thetetrahydro compound normally does not begin until after the originaldicyclodiene acid salt was completely converted to the dihydroderivative.

In producing the dihydro derivative it is advisable to aersgnao 5 keepthe reaction temperature between ahqut-.2 and 70 C., preferably betweenabout 40 and 360 C.,-inorder .to minimize cracking and production of.themalodorous monomeric hydrogenated acid, i.e. cyclopentane carboxylicacid. The same temperature .conditionsare desirable in the initialstages even when production of the tetrahydro derivative is desired.That is,-it .is best toprepare first the dihydro derivative at themoderate temperatures indicated and then raise the temperatureto about100 to 200 C., in order to convert the dih'y'droto the tetrahydroderivative. While preparation of the tetrahydro derivative is-possibleat the same low temperature that suitable for preparing the dihydroderivative, the rate of hydrogenation to the tetraliyfdro stage is veryslow under those conditions. On the other hand, since'the dihydroderivative itself is quite stable and not readily cracked, it is"advantageous .to carry out'the 'secondhy'drogenation stage ata highertemperature as indicated above. Reniember'in'gthat the exactpositionofthe'carboxyl groups has not been definitely established thetwohydrogenation stages canbe 'illustrated'by" the following equations:

Disodlum'salt of Tetrahy'drodicyclopentadiene dlearboxylic acid Ofcourse, the reaction proceeds similarlylwhen the correspondingderivatives of .methylcyclopentadiene or the like are being treated.

The hydrogenationiscarried out at hydrogen pressures which may rangefrom about atmospheric to 2000 p. s. i. .g. depending on the particularcatalyst -used, etc., preferably about 400 to 1000 p. s. i. g. with -anickel catalyst. A hydrogenation catalyst such as Adams platinum oxide,Raney nickel, nickel on a support such as alumina, silica, kieselguhr'oractivated carbon, cobalt,- palladium, iron or generally metals of groupsI -Band VIII of the periodic table, either inclemental ;-form or asreducible oxides, are suitable for use-in the present invention.

When a supported catalystis used the aqueous salt solution can be passedover the catalyst countercurrent to the hydrogen. In such .a process'itthen becomes unnecessary to filter off and recover suspended catalystfrom the hydrogenated salt solution prior to springing 6 the -free acidtherefrom. The catalyst may be used in 'an-amountof about 0.5 to percentexpressed as elemental metal based on the dicarboxylated dicyclodienesalt.

Several specific examples will now 'be given for the purpose ofillustrating the advantages of the invention and of further facilitatingits practice by others, although it will be understood that-theinvention isnot limited'ther'eto.

EXAMPLES In each case summarized in Table I the originaldicarboxylateddicyclopentadiene feed used in the hydrogenation was prepared asfollows: I

150g. of cyclopentadiene monornerwa's added d'ropwise to 46 g. of sodiumdispersedin :600'mluof-xylene, activated with 3 ml. of 99% isopropylalcohol. The

1 temperature was maintained at 40 C. by intermittent cooling. In thismannera dispersion.ofcyclopentadienyl sodium in xylene was obtained.

The resulting cyclopentadienyl sodium was "carboxylated by slowlyadding, over a period of 90 minutesft'he aforementioned cyclopentadienylsodium dispersion to 1 liter of xylene kept saturated with CO atessentially atmospheric pressure and -20 C. The carboxylatedcyclopentadienyl sodium slurry was then added .to about 1500 ml. ofwater and the aqueous salt solution was separated from the organicxylene layer. For premium quality products it may also be advantageousto "acidify the water with sulfuric or acetic acid or the like beforeaddition of the organic salt slurry in order to keep the pH of theresulting aqueous salt solution in thepreferred pH range of about 5.8 to'7 .as described'in cope'nding application Serial No. 515,255, filedJune 13, 1955.

In runs 1 and 3 the pH of the carboxylated salt solution was adjusted to7.2 to 7.5 by the addition of a small amount of dilute sulfuricacid'a'nd the acidified solution was allowed to stand for four days atroom'temperature in order to make certain that the carboxylatedcyclodiene salt was completely dimerized before it was used forhydrogenation. In runs 2 and 4 the hydrogenation feed consisted of theincompletely hydrogenated product from runs 1 and 3, respectively. Inruns 5-8 the hydrogenation feed was obtained by first acidifying theaqueous salt solution with 50% H filtering off the precipitated freedicarboxylic dicyclopentadiene acid, and neutralizing the solid acidwith dilute sodium hydroxide "to the pH value indicated in Table I. Inrun 9 the aqueous carboxylated dicyclodiene salt solution was used forhydrogenation immediately after its separation from the organic xylenelayer, without any intervening aging or pH adjustment.

The hydrogenations were run in a 1.4-liter rockerbomb using 10% Raneynickel catalyst based on the dicarboxylic acid salt. In each case about1000 g. of the aqueoussalt solution, containing about 20 to 30% of thesalt, were charged to the bomb, the catalyst was added, the bomb flushedwith hydrogen, and then charged with hydrogen and heated under theconditions sepecified in Table I. Where only the dihydro derivative wasdesired, it was found that better control was obtained by heating theopen bomb to reaction temperature before pressuring with hydrogen, sincein this manner the hydrogen consumption could be followed more exactlythan when the bomb was pressured at room temperature. At the end of therun the pressure was released, catalyst filtered ofi, and'the filtrateacidified with 50% sulfuric acidto reduce the pH to about 3 to 4.The'resulting precipitated free Table I.Hydrogenatln of dzsodzum salt ofdzcyclopentadzene dzcarboxyllc (161d 7.2-7 4 7.a 6.8. 150- 45.- 93 45.Pressure range, p. s. i. g. 1,5001,700 1,465-1 4 1,4851,44fl1,400-1,330. Contact time, hrs 2.10 2.00 0.50 2.75. Crystallizationbehavior Tafiy hardens mins. Tafiy hardens mins. Taiiy hardens 301111115. Hard granules. Color salt solution Lt. brown Pale yellow Paleyellow. Color dry acid Cit-white Off-white White. Odor dry acid M 1mMild Very slight. Yield, wt. percent... so 95 96. Acid No., ceqJg 0.8870.882 0.867. Percent of theoretical 98.5-- 98.2... 95.8. Bromine N 0.,cg. Bra/g .0 111.0. Moles H2 added/mole of dicyclo- 60 0.50.

pentadiene dicarboxylic acid.

Run No 6 7 8 9 Feed pH Salt iced 8.0 8.0 6 8 11.0. Reaction temp., C 770 27-45 Pressure range, p. s. i. g 1,3201,250 l,4001,305 1,4051,3051,400-1,160. Contact time, hrs 1.25 2.15 1.5 0.92 Crystallizationbehavior Tady hardens 30 ruins. Taffy hardens 90 mins- Tafiy hardens 90mius. Taffy hardens 20 mins. Color salt solution B Dark brown YellowBrown. Color dry acid.-. Tan Off-whim l .t. tan. Odor dry aeid Strong-Moderate Very strong. Yield, wt. percent. 80 80 76.0. Acid N o., ceqJg0.879 0.880 0.880 Percent of theoretical- 97.6.. 97.7 98.1. Bromine No.,cg. Bra/g 8 72.6. 01 0 17.9. Moles H7 added/mole of dioyclopentadienedicar- 1.00- 1 20 1.75.

boxylic acid.

()N& salt direct from carboxylation, not allowed to dimerize. )Na saltdirect from carboxylation, dimerized for 14 days. ()Acid from run 1neutralized with dilute N aOH.

( )Acid from run 8 neutralized with dilute N 21011.

( Free unhydrogenated acid neutralized with dilute NaOH.

( )Hz on bomb during warm-up to 45 C. Warm-up included in contact timegiven.

()Tafiy-like products seeded to aid crystallization.

The data show the effectiveness of the present invention andparticularly demonstrate the advantages in product quality when thehydrogenation is done at pH values below 7.5. Runs 2 and 4 illustratethe advantages of carrying the second hydrogenation stage at moreelevated temperatures. Run 2 in particular shows the conversion of anincompletely hydrogenated product into a completely saturated one attemperatures above 150 (3., without any unwanted side eflects. On theother hand, if the hydrogenation is done at such a high temperature fromthe beginning, a malodorous, dark colored product will result due tocracking. In run 9 a low yield of poor quality product was obtained dueto the presence of monomeric cyclopentadiene carboxylic acid in thefeed. The resulting cyclopentane monocarboxylic acid is rnalodorous and,being substantially water soluble, accounts for the relatively pooryield of product subsequent to washing with water. However, thisdisadvantage can be avoided by aging the unsaturated salt at moderatetemperatures, e. g. at 0 to C., for a sufficient time to causesubstantially complete dimerization of any monomeric salt prior tohydrogenation. This is illustrated in runs 1 and 3. Furthermore, anysuch difliculties are usually avoided altogether when the unsaturatedcarboxyiic salt is first converted into free acid and the latter isredissolved in dilute alkali prior to the hydrogenation, as illustratedin runs 5-8.

The scope of the invention is particularly pointed out in the appendedclaims, especially when read with reference toand in the spirit of theforegoing description and the state of the art.

What is claimed is:

1. A process for hydrogcnating a water soluble metal salt of adicarboxylated dicyclopentadiene acid which comprises forming an aqueoussolution of said salt adjusted to a pH value between about 5.8 and 7.5and contacting the aqueous solution with hydrogen under pressure at atemperature below C. in the presence of a hydrogenation catalyst untilat least about one mole of hydrogen is reacted per mole of said salt.

2. A process for preparing hydrogenated derivatives of a dicarboxylateddicyclopentadicue acid which comprises forming an aqueous solution of analkali metal salt of said acid, contacting said solution with hydrogenat an efiective hydrogenation pressure in the range between 0 and 2000p. s. i. g. in the presence of a hydrogenation catalyst at a temperaturebetween about 20 and 70 C. until at least about one mole of hydrogen isreacted per mole of said salt, separating the catalyst from the aqueoussolution, acidifying the catalyst-free solution to precipitate freehydrogenated dicarboxylated acid therefrom, and separating theprecipitated acid from the solution.

3. A process according to claim 2 wherein the initial dicarboxylatedacid is dimethyldicyclopentadiene dicarboxylic acid.

4. A process according to claim 2 wherein the initial dicarboxylatedacid is dicyclopentadiene dicarboxylic acid.

5. Aprocess according to claim 4 wherein the hydrogenation temperatureis raised above C. after about the first mole of hydrogen is reacted permole of salt and the hydrogenation is continued at the increasedtemperature until about another mole of hydrogen is reacted per mole ofsalt.

6. A process according to claim 5 wherein the hydrogenation catalyst isRaney nickel.

7. A process according to claim 5 wherein the hydrogenation catalyst isnickel deposited on kieselguhr.

8. In combination with a process wherein cyclopentadiene is reacted withan alkali metal in the presence of an inert hydrocarbon diluent to forma hydrocarbon slurry of a cyclopentadienyl metal compound, and thecyclopentadienyl metal compound is carboxylated in the slurry withcarbon dioxide to form a hydrocarbon slurry of a metal salt ofdicyclopentadiene dicarboxylic acid, the improvement which comprisesmixing the hydrocarbon slurry of the salt with extraneously acidifiedwater to form an aqueous solution of said metal salt, the amount ofextraneous acid added being suflicient to form an aqueous solutionhaving a pH between 5.8 and 7.0 when mixed with said salt, separatingthe hydrocarbon diluent from the acidified aqueous salt solution, agingthe separated aqueous salt solution until any monomeric carboxylic saltis dimerized, adding a hydrogenation catalyst to the aged aqueoussolution, contacting said aqueous solution with hydrogen at an eflectivehydrogenation pressure in the range between about 400 and 2000 p. s. i.g. at a temperature between about 30 and 60 C. until about one mole ofhydrogen is absorbed per mole of dissolved salt, then raising thetemperature of the solution toabout 100 to 200 C. and continuing thehydrogenation until the dissolved salt is substantially completelysaturated, separating the catalyst from the solution, acidifying thesolution to a pH of about 3 to 4 so as to precipitate free hydrogenatedacid from the solution, and recovering said hydrogenated acid.

9. A process according to claim 8 wherein the extraneous acid is glacialacetic acid.

10. A process according to claim 8 wherein the extraneous acid'isconcentrated sulfuric acid.

11. A process for preparing hydrogenated dicarboxylic acids whichcomprises partially neutralizing solid dicyclopentadiene dicarboxylicacid with dilute alkali to form an aqueous solution having a pH valuebetween about 5.8 and 7.5, contacting this solution in the presence of anickel hydrogenation catalyst with hydrogen under a pressure of about400 to 1000 p. s. i. g. at a temperature between about and C. until atleast about one mole of hydrogen is absorbed per mole of dissolved salt,separating the catalyst from the reaction mixture, acidifying theremaining aqueous solution to a pH below 4 in order to precipitate freehydrogenated dicyclopentadiene dicarboxylic acid, and separating theprecipitated acid from the solution.

References Cited in the file of this patent UNITED STATES PATENTS1,877,991 Schwenk Sept. 20, 1932 2,675,390 Rosenblatt Apr. 13, 19542,688,627 Cohen et al. Sept. 7, 1954 2,716,662 Cohen et al. Aug. 30,1955

